Microsoft is teaming up with rival Google in legal action against the US government after talks to allow the companies to tell their users if they are being spied upon broke down.

"There are many days when Microsoft and Google stand apart. But today our two companies stand together," said Redmond's general counsel Brad Smith on a blog post. "We both remain concerned with the Government's continued unwillingness to permit us to publish sufficient data relating to Foreign Intelligence Surveillance Act (FISA) orders."

Both Google and Microsoft filed petitions with the government in June asking to be more open about the amount of data they were required to hand over to government investigators via secret court orders, details of which were revealed by Edward Snowden. Since then, Smith said, Microsoft has agreed to extend the deadline for a response from the government six times, to no avail.

Earlier this week, the government said that it would begin publishing an annual report stating how many national security requests it puts out every year. Smith said this was a good start but that it didn't go far enough. The two firms want the government to allow the publication of more detailed information, for example when requests for email content are sent out.

"While the government's decision to publish aggregate information about certain national security requests is a step in the right direction, we believe there is still too much secrecy around these requests and that more openness is needed," a Google spokesman told The Register in a statement.

"That's why we, along with many others, have called on the U.S. government to allow us to publish specific numbers about both FISA and NSL requests."

Both companies are concerned that the continuing uncertainty about exactly what information the government is demanding, and how often, is hurting their business – specifically their cloud services. A recent study found that disclosures of the NSA spying program could cost US businesses between $22bn and $35bn over the next three years.

"We benefit from living in a country with a Constitution that guarantees the fundamental freedom to engage in free expression unless silence is required by a narrowly tailored, compelling Government interest. We believe there remains a path forward that will share more information with the public while protecting national security," Smith concluded. ®